Apparatus and method for terminating film resistors



June 6 1967 c. .J. MELLAR ETAL. 3,323,492

APPARATUS'AND METHOD FOR TERMINATING FILM RESISTORS Filed Sept. 12, 1965 4 Sheets-Sheet 1 IN VEN TORS CARROLL J. MELLAR JOHN G. KIRSCHNER ROBERT WIENER ROLAND H. McCLELLAND ATTORNEY June 6, 19%? G. .J. MELLAR ETAL APPARATUS AND METHOD FOR TERMILIATING FILM RESISTORS Filed Sept. 12, 1965 4 Sheets-She'h LZWVENTOHS CARROLL J. MELLIKR JOHN G. WRSCHNEFZ ROBERT WITENER NOLAN D H. MQQLELLAND June 6, 1967 c. J. MELLAR ETAL. 3,

APPARATUS AND METHOD FOR TERMINATING FILM RESISTORS Filed Sept. 12, 1963 4 Sheets-Sheet 5 INVENTORS I -32 CARROLL .1. MELLAR JOHN G, KIRSCHNIER V ROBERT WIENER F1 6. 4

RQLAND H. McCLELLAND ATTORNEY June 6, 1967 c. J. MELLAR ETAL APPARATUS AND METHOD FOR TERMINATING FILM RESISTORS 4 Sheets-Sheet 4 Filed Sept. 12, 1963 IN VEN TORS CARROLL J. MELLAR JOHN G. KIRSCHNER ROBERT WIENER ROLAND H. McCLELLAND 4Q BY CD ATTORNEY United States Patent 3,323,492 APPARATUS AND METHUD FOR TERMINATING FILM RESISTORS Carroll John Mellar, Chicago, .lohn G. Kirschner, Niles,

Robert Wiener, Highland Park, and Roland H. McClelland, Deerfield, Iil., assignors to P. R. Mallory & C0., l'nc., Indianapolis, Ind., a corporation of Delaware Filed Sept. 12, 1963, Ser. No. 308,406 9 Claims. (Cl. 118-620) ABSTRACT OF THE DISCLOSURE An apparatus for applying solderable end terminations on film resistors so that the electrical properties of the resistive film are not degraded by the process. A liquid conductive medium is applied to the ends of the resistive body and after a drying operation, the resistors are passed through the convolutions of an induction heating coil at a determined rate so as to fire the conductive medium. The heat generated by the induction heating coil is localized at the resistor ends by the convolutions of the heating coil While the resistor body is maintained relatively cool. The resistive film does not have its electrical properties degraded during firing.

This invention relates to the means and method for terminating electrical components and has specific pertinence to an apparatus and method for applying and firing solderable silver electrode terminals on metal oxide film resistors without degrading the resistive film.

A method of terminating film resistors which is well known in the art comprises the attachment of a metal adapter to the ends or edges of the resistor. Where the resistor substrate is a cylindrical rod of ceramic material having a resistive coating applied to the surface thereof, termination may be effected by the addition of metal caps to the rod ends. The terminal caps may be applied directly onto the resistive film while relying on pressure to maintain adequate contact. In another construction, the terminal caps may be applied over a graphited rod. In still another construction they may be attached to an electrode which is formed on the resistor by electroplating, electroless plating, or baked conductive paint.

The use of metal end cap electrodes is not advantageous, however, in certain resistor applications. For example, when the film resistor has very small dimensions, the attachment of individual end caps is both tediou and expensive. Furthermore, when a group of small resistors is arranged in an electrical network, the individual terminals will sometimes be soldered to a silvered patch on a ceramic substrate plate. The network leads are thereupon soldered to the silvered patches at appropriate points. In such a network construction, therefore, significant savings could be realized if the need for terminal end caps were obviated.

One proposed substitute for metal end caps is found in conventional electroless plated terminations. This expedient i not fully satisfactory because, besides involving complicated processing techniques, the resulting terminals are not well adapted to soldering. The use of silver for termination of a film resistor has particular advantage because of its adaptability to soldering. When provided in the form of silver paint, it is applied to the resistor ends 'by spraying or dipping, and thereupon fired within a kiln. It has been found, however, that when silver is applied to a metal oxide film resistor and then subjected to kiln firing, the electrical properties of the oxide film are degraded.

It is highly desirable, therefore, to provide a means of economically terminating a film resistor wherein the elecice trical characteristics of the film are not impaired by the termination process, and wherein the resulting terminal is readily solderable and possesses good mechanical properties. By the present invention there is provided an apparatus and method which achieves the desired result. This device is adapted to apply a water base silver paint to the ends of a metal oxide film resistor having substantially cylindrical shape. The paint is then dried, and thereupon fired by means of induced radio-frequency heating to form a soldera-ble silver end termination. The frequency level of the induced current is chosen so as to correspond with that frequency at which the silver paint exhibits its most lossy electrical properties. Thus, the resulting energy loss will appear as localized heat of sufiicient intensity to effectively fire the end terminations. The geometry of the induction heating member i carefully controlled to afford optimum localization of heat at the resistor ends. During the firing process, the main body of the resistor is cradled within a conveyance member having high thermal conductivity such that an efiicient heat sink is provided. The conveyance member itself does not attain an unduly high temperature level largely because of the frequency of in duced current and the positioning with respect to the heating member. The resistor body, therefore, experiences no deleterious heat rise while the end terminals are being fired. The electrical properties of the resistive film are in no way degraded, and the resulting termination is mechanically strong. The process is fully automatic, the production capabilities are high, and the device fetature mechanical simplicity.

It is an object of the present invention, therefore, to provide the means and method for applying solderable silver end terminations on electrical components.

It is a further object of the present invention to provide the means and method for applying and firing solderable silver end terminations on metal oxide film resistors wherein the electrical properties of the resistive film are not degraded.

Another object of the present invention is to provide an induction heating member of determined geometry which efiiciently fires the silvered end terminations without causing undue heat rise in the main body of the resistor.

Yet another object of the present invention is to provide current to the induction heating member at that frequency where the silvered end terminations exhibit their most lossy electrical properties.

Still another object of the present invention is to provide a continuous process apparatus which automatically applies, dries, and fires silver electrode terminations on electrical components.

Yet another object of the present invention is to provide an apparatus which produces fired-on silver electrode terminations having excellent mechanical properties and superior ohmic contact.

Still another object of the present invention is to provide a unitized device having a plurality of work stations cooperating to automatically and eificiently produce silver electrode terminations having superior properties. Synchronism of the silvering wheel and carrier wheel velocities is positively assured through a simple gear train.

Yet another object of the present invention is to provide an efiicient and accurate means of locating and advancing the electrical components which are to be terminated by this apparatus.

Still another object of the present invention is to provide a simple but effective means of automatically introducing silver paint in the desired amounts on the component to be terminated.

Still another object of the present invention is to pr0- vide a method of firing the applied silver paint wherein the electrical and mechanical properties of the component are not diminished.

The present invention, in another of its aspects, relates to novel features of the instrumentalities described herein for teaching the principal object of the invention and to the novel principles employed in the instrumentalities whether or not these features and principles may be used in the said object and/or in the said field.

Other objects of the present invention and the nature thereof will become apparent from the following description considered in connection with the accompanying figures of the drawing and wherein like reference characters describe elements of similar function therein, and wherein the scope of the invention is determined rather from the dependent claims.

In the drawings:

FIGURE 1 is a perspective view, partially cut away, of the terminating apparatus taught by the present invention.

FIGURE 2 is a side elevational view showing the several work stations employed in the terminating apparatus of the present invention.

FIGURE 3 is a fragmentary elevational view of the two applicator wheels used for introducing silver paint onto cylindrical resistor bodies.

FIGURE 4 is a sectional view of the peripheral portion of one applicator wheel, taken along line 44 of FIG- URE 3, showing silver paint retained within the circumferential groove.

FIGURE 5 is a fragmentary perspective view showing the induction heating coil used for firing the silver terminations on cylindrical film resistors.

Generally speaking, the present invention provides the means and method for efficiently applying solderable end terminations on film resistors wherein the electrical properties of the resistive film are not degraded by the process. A conductive paint, preferably of silver, is applied to the ends of a film resistor body. After a drying operation, the resistors are passed within an induction heating coil at a determined rate wherein the termination is fired. By proper choice of induced current frequency and heating coil configuration, the generated heat is localized at the resistor ends while the resistor body is maintained relatively cool. The resistive film, therefore, is not diminished in its electrical characteristics.

Referring now to FIGURES 1 and 2 of the drawings, the apparatus of the present invention is indicated generally by reference numeral 10. The resistor bodies to be terminated, shown typically at 11, are initially contained within vibratory parts feeder 12. Metal oxide film resistors having cylindrical dimensions of V inch diameter by inch long are typical of the components adaptable to the present invention. By a vibratory action, the bodies are urged through guide tube 13 into a stacked position Within feed member 14. As resistor body 11 descends by gravity through feed member 14, it is attracted by suction to a firm position within one of a plurality of peripheral grooves 15 in slowly rotating vacuum wheel 16. Vacuum wheel assembly 16 is composed of copper rim 17 supported by two flanged aluminum half shells, shown typically at 18. The body of wheel 16 is hollow and adapted to function as a vacuum chamber. Rim 17 contains a series of radial vacuum holes, one for each peripheral groove 15. Vacuum pump 19, which is driven by electric motor 18, serves to evacuate wheel assembly 16 through hose 21 and a rotatable vacuum seal attached to the center of the aluminum half shell. With a wheel diameter of approximately 14 inches, 270 resistors of the above-stated size may be simultaneously accommodated.

With continued reference to FIGURES 1 and 2, rotation of vacuum wheel assembly 16 is provided by vari able speed motor 22, the output of which engages speed reducer 23. To the output shaft of speed reducer 23 is affixed drive pulley 24 which transmits motion through V-belt 25 to driven pulley 26. Pulley 26 is rigidly attached to one end of drive shaft 27 and support for the shaft at that end is afforded by bushing 28 disposed within vertical plate 29. The other end of drive shaft 27 is atfixed to the center of aluminum half shell 18. Supp rt for the rotating assembly in that region is provided on the opposite side of vacuum wheel 16. The main drive assembly is housed by shroud member 30.

As vacuum wheel 16 rotates in the direction indicated by the arrow, resistor body 11 is transported from the feed mechanism to a pair of circumferentially-grooved applicator wheels 31 and 32. The applicator wheels are placed tangentially at the circumference of vacuum wheel 16 in a plane perpendicular to that of the latter. Applicator wheels 31 and 32 are synchronously driven from drive shaft 27 with a peripheral linear velocity matching that of vacuum wheels 16. Bevel drive gear 33 is afiixed to drive shaft 27 at a position adjacent to vacuum wheel 16. Meshing with bevel gear 33 is a bevel pinion 34 attached to applicator shaft 35. Piloting of shaft 35 on the pinion end is afforded by bracket and bushing member 36. To provide synchronism and counter-rotation of applicator wheel 32 with respect to applicator wheel 31, a four-element gear train is furnished. Drive gear 37, which is atfixed to applicator shaft 35, drives two idler gears which are cantilever-mounted on idler posts 38 and 39, respectively. Applicator wheel 32 is thereupon rotated by a gear concentrically disposed on idler post 40. Structural support for the applicator wheel and gear assembly is afforded by vertical plate 41 which, like the other stationary components of apparatus 10, is affixed to baseplate 42. Housing 43 shrouds the gear assembly.

With further reference to FIGURES 1 and 2, as applioator wheels 31 and 32 continue to rotate, the peripheral portions thereof are immersed in the water-base silver paint 61 contained in supply tank 44. In order to remove the excess paint adhering to the rotating wheels as they emerge from tank 44, an adjustable wiper 45 is provided on each end of tank cover 46. The silver paint which remains in the circumferential groove of applicator wheels 31 and 32 is retained therein by capillary action as the wheels rotate. This paint is thereupon applied to each end of resistor bodies 11 as the bodies are advanced by vacuum wheel 16. Functional details of this application of silver will be discussed later with reference to FIG- URE 3. To insure a satisfactory degree of uniformity in the silvering pattern, on the resistor bodies, the silver paint 61 within tank 44 is continually agitated by means of motor 47 and paddle 64 to prevent settling. Futhermore, the viscosity of the solution is carefully controlled therein.

After silver paint 61 is applied to the ends of the resistor bodies by applicator wheels '31 and 32, it is dried by means of resistance heating element 48 which is located beneath vacuum wheel 16. Visible in FIGURE 2 is a pair of guide rollers shown typically at 58, used for axial alignment of the resistor bodies after they pass heating element 48.

The final processing step in the apparatus of the present invention provides means for firing of the silvered ends of the resistor bodies. Induction heating coil 49 is energized at a radio frequency of 2.3 megacycles, and the current flow induced in the silver paint creates localized heat sufiicient to fire the resistor ends. Details of induction heating coil 49 will be discussed later with reference to FIGURE 5. Power supply and water cooling provisions for induction heating coil 49 are contained within housing 50.

As the resistors approach one complete revolution on vacuum wheel 16 and are completely terminated, they are automatically released from vacuum retention by two rojecting fingers on spring clip 51. As each resistor is stripped from vacuum wheel 16, it is urged to descend exit tray 52 into chute 53, and thereupon into bin 54. Mechanical support for the removal system is afforded by vertical member 55 and horizontal member 56. As each departing resistor ascends upon the inclined fingers of spring clip 51, it deflects the upper end of exit tray 52 which is allowed to pivot about hanger 57 for this purpose.

FIGURE 3 illustrates details of the silver paint application station. At the bottom of the circumferential groove in applicator wheels 31 and 32 is disposed rubber band 60. This can be seen more clearly in FIGURE 4, which is a sectional view through the peripheral portion of applicator Wheel 32 in FIGURE 3. Disposed radially outward from rubber band 60 is a quantity of silver paint 61. Retention of silver paint '61 within the rotating wheel groove is eifected by capillary action.

Referring again to FIGURE 3, as resistor body 11 is lowered by vacuum wheel 16, it is first brought in contact with silver paint 61, after which the resistor ends deflect opposed rubber bands 60. In addition to centering the resistor bodies during silvering, the resilience of rubher hands 60 forces silver over the resistor ends in the desired quantity, as shown by reference numeral 62.

FIGURE 5 presents a detailed view of induction heating coil 49, together with a fragmentary sectional view of vacuum wheel 16. As the silvered ends 62 of resistor body 11 are advanced upward by vacuum wheel 16 into the convolutions of coil 49, a current is induced in the silver paint. Since the paint has lossy electrical properties at the 2.3 megacycle frequency, the energy loss appears as heat which fires silvered end 62, yielding a solderable termination. Through the tubing of coil 49 is flowed a sutficient quantity of cooling water.

The firing system illustrated in FIGURE 5 is outstanding because the main body of resistor 11 is heated to a level only slightly higher than that experienced during the drying operation of resistance heating element 48. This effect is attributed to several factors. First at all, because of the excellent heat transfer characteristics of copper rim 17, a natural heat sink is provided for that portion of resistor body 11 which is gripped within groove 15. Secondly, due to the positioning of induction heating coil 49 with respect to copper rim I7, and to the particular frequency employed, the heat rise within rim 17 is relatively low. The excellent mechanical properties of copper rim 17 make it further attractive for this application.

Certain design criteria must be observed to assure successful firing by the method of the present invention. Proper firing by radio frequency induction heating depends to a great extent upon correct design relationships between the R-F output coil and the geometric construction of the part to be silver-fired. FIGURE 5 illustrates the particular design of coil 49 employed for a cylindrical resistor having proportions shown therein. A change in resistor configuration would ordinarily require a change in coil configuration. It has been found that satisfactory solderability properties tend to correlate with the visual appearance of resistor ends 62 as they are being fired. As they pass through induction heating coil 49, they glow to a red coloration, then decrease in luminosity.

It is conceivable that materials other than copper could be employed for rim 17. Such material, however, would have to withstand the induction heating without overheating or dissipating excessive energy. Furthermore, it must not distort the electromagnetic field in a manner which prevents said field from firing the silvered resistor ends 62. It is also conceivable that a material other than silver could be used for end termination 62; however, it would have to absorb and dissipate enough energy to fuse to a solderable state.

The vehicle or base in which the silver paint is applied must not be excessively insulative in the unfired state, as are many of the non-aqueous resin base silver paints. If too highly insulative, the termination will have insufficient conductivity to incur the eddy current losses necessary for proper induction firing. In order tobe properly dried prior to firing, the silver paint should have a rapidly evaporable vehicle.

Due to the thermal shock incurred in relatively cool resistor body 11 as the silvered ends 62 are fired to a high temperature, it is necessary to employ a substrate material which can resist thermal fracture. It has been found that steatite affords excellent properties in this respect.

Referring once again to FIGURE 5 of the drawing, the fragmentary sectional view through vacuum wheel 16 discloses radial vacuum hole 63 which extends outwardly through copper rim 17 into peripheral groove 15. Hole 63, as hereinbefore mentioned, communicates sufficient vacuum to retain resistor 11 while it rotates with rim 17.

The film resistor terminating apparatus and method of the present invention, as hereinbefore described in one of its embodiments, is merely illustrative and not exhaustive in scope. Since many widely different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interposed as illustrative and not in a limiting sense.

What is claimed is:

1. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a rotatable main wheel having a plurality of spaced peripheral serrations, feed means for introducing said resistors into said serrations, means retaining said resistors in said serrations, applicator means for applying a conductive liquid medium onto the ends of each of said resistors, said applicator means comprising a plurality of rotating wheels, means for introducing said conductive liquid medium into a circumferential groove carried by each of said plurality of Wheels, said conductive liquid medium retained in said grooves by capillary attraction, means disposed adjacent the base of each of said grooves and adapted to place said conductive liquid medium over said resistor ends as said plurality of wheels rotate thereover, a heating element adjacent said main wheel adapted to dry said conductive medium on the ends of said resistors, and induction heating coil means firing said conductive medium to form a solderable termination On each end of said resistor without degrading the resistive film of said resistors, and tripping means attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

2. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a rotatable main wheel having a plurality of spaced peripheral serrations, feed means for introducing said resistors into said serrations, means retaining said resistors in said serrations, applicator means for applying a conductive liquid medium onto the ends of each of said resistors, said applicator means comprising a plurality of rotating wheels, means for introducing said conductive liquid medium into a circumferential groove carried by each of said plurality of wheels, said conductive liquid medium retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive liquid medium over said resistor ends as said plurality of wheels rotate thereagainst, a heating element adjacent said main Wheel adapted to dry said medium on the ends of said resistors, and induction heating coil means firing said conductive medium to form a soldera ble termination on each end of said resistor without degrading the resistive film of said resistors, and tripping means at tached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

3. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a rotatable rnain wheel having a plurality of spaced peripheral serrations, feed means for introducing said resistors into said serrations, means retaining said resistors in said serrations, applicator means for applying a conductive liquid medium onto the ends of each of said resist-ors, said applicator means comprising a plurality of counter-rotating wheels disposed on either side of said conveyance means, means for introducing said conductive liquid medium into a circumferential groove carried by each of said counter-rotating wheels, said conductive liquid medium retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive liquid medium around said resistor ends as said counter-rotating wheels rotate thereagainst, a heating element adjacent said main wheel adapted to dry said medium on the ends of said resistors, and induction heating coil means firing said conductive medium to form a solderable termination on each end of said resistor without degrading the resistive film of said resistors, and tripping means attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

4. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a rotatable main wheel having a plurality of spaced peripheral serrations conforming generally to the contour of said resistors, feed means for sequentially introducing said resistors into said serrations so that the longitudinal axis of each of said resistors is substantially parallel to the rotational axis of said main wheel, vacuum means retaining said resistors in said serrations, applicator means for applying conductive paint onto the ends of each of said resistors, said applicator means comprising a plurality of counter-rotating wheels disposed on either side of said conveyance means, means for introducing said conductive paint into a circumferential groove carried by each of said counter-rotating wheels, said conductive paint retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive paint around said resistor ends as said counter-rotating wheels rotate thereagainst, a heating element adjacent said main wheel adapted to dry said paint on the ends of said resistors, and induction heating coil means firing said conductive paint to form a solderable termination on each end of said resistor without degrading the resistive film of said resistors, and tripping means attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

5. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a rotatable main wheel having a plurality of spaced peripheral serrations conforming generally to the contour of said resistors, feed means for sequentially introducing said resistors into said serrations so that the longitudinal axis of each of said resistors is substantially parallel to the rotational axis of said main wheel, vacuum means retaining said resistors in said serrations, applicator means for applying conductive paint onto the ends of each of said resistors, said applicator means comprising a plurality of counter-rotating wheels disposed on either side of said conveyance means for introducing said conductive paint into a circumferential groove carried by each of said counter-rotating wheels, said conductive paint retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive paint around said resistor ends as said counterfrotating wheels rotate thereagainst, a heating element adjacent said main wheel adapted to dry said paint on the ends of said resistors, and induction heating coil connected to a radio frequency current source emitting a predetermined frequency, said coil being adapted to fire said paint to form a solderable termination on each end of said resistor without degrading the resistive film of said resistors, and tripping means attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

6. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a hollow rotatable main wheel including a copper rim having a plurality of substantially equally-spaced peripheral serrations conforming generally to the contour of said resistors, feed means for sequentially introducing said resistors into said serrations so that the longitudinal axis of each of said resistors is substantially parallel to the rotational axis of said main wheel, a radial passage extending from the base of said serrations to an evacuated chamber formed within said main wheel, said vacuum retaining said resistors in said serrations, applicator means for applying conductive paint onto the ends of each of said resistors, said applicator means comprising a pair of counter-rotating wheels synchronously driven by said conveyance means and disposed on either side thereof, means for introducing said conductive paint into a circumferential groove carried by each of said counterrotating wheels, said conductive paint retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive paint around said resistor ends as said counter-rotating wheels rotate thereagainst, a heating element adjacent said main wheel adapted to dry said paint on the ends of said resistors, and induction heating coil connected to a radio frequency current source emitting a predetermined frequency, said coil being adapted to fire said paint to form a solderable termination on each end of said resistor without degrading the resistive film of said resistors, and tripping means attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

7. In an apparatus for terminating film resistors without degrading the resistive film, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, said conveyance means comprising a hollow rotatable main wheel including a copper rim having a plurality of substantially equallyspaced peripheral serrations conforming generally to the contour of said resistors, feed means for sequentially introducing said resistors into said serrations so that the longitudinal axis of each of said resistors is substantially parallel to the rotational axis of said main wheel, a radial passage extending from the base of said serrations to an evacuated chamber formed within said main wheel, said vacuum retaining said resistors in said serrations, applicator means for applying conductive silver paint onto the ends of each of said resistors, said applicator means comprising a pair of counter-rotating wheels synchronously driven by said conveyance means and disposed on either side thereof, means for introducing said conductive silver paint into a circumferential groove carried by each of said counter-rotating wheels, said conductive silver paint retained in said grooves by capillary attraction, a resilient circumferential band disposed adjacent the base of each of said grooves and adapted to squeeze said conductive silver paint around said resistor ends when said resistor ends are enveloped by said grooves as said counter-rotating wheels rotate, a heating element adjacent said main wheel adapted to dry said silver paint on the ends of said resistors, and an induction heating coil including convolutions connected to a radio frequency current source emitting a frequency at which said silver paint exhibits poor electrical properties, said coil being adapted to fire said paint to form a solderable termination on each end of said resistor without degrading the resistive film of said resistors as said silver painted ends of said resistors pass through said oonvolutions of said heating coil, and tripping mean attached to remove said resistors having solderable end terminations from said main wheel prior to reaching said feed means.

8. In an apparatus for terminating metal oxide film resistors, conveyance means for advancing said resistors at a determined rate through a plurality of work stations, applicator means adapted to deposit a conductive paint onto the ends of said resistors, said applicator means comprising a pair of counter-rotating wheels synchronously driven by said conveyance means and disposed on either side thereof, means for introducing said conductive paint into a circumferential groove within each of said wheels, a resilient circumferential band disposed adjacent the base of said groove and adapted to squeeze said paint around the resistor ends as said wheels rotate thereagainst, a resistance heating element adjacent said conveyance means adapted to dry said paint as said resistors advance therethrough, and an induction heating coil having a current source of determined frequency, said coil being adapted to fire said paint to form a solderable termination without degrading the metal oxide resistive film.

9. In an apparatus for terminating film resistors, a hollow rotatable main wheel having a plurality of equally spaced peripheral serrations conforming generally to the contour of said resistors, feed means for sequentially introducing said resistors into said serrations such that the longitudinal axis of said resistors is substantially parallel to the rotational axis of said main wheel, a radial passage from the base of each of said serrations communicating with an evacuated chamber Within said main wheel to retain said resistors in position, a pair of counter-rotating applicator wheels cooperating with said main wheel and adapted to deposit a silver paint onto the ends of said resistors, a heating element adjacent said main wheel adapted to dry the deposited paint, a water-cooled induction heating coil having a radio-frequency current source, said coil being adapted to fire said paint to form a solderable termination without degrading the resistive film, and a tripping member adapted to remove said resistors from said main wheel prior to reaching said feed means.

References Cited UNITED STATES PATENTS 1,409,676 3/1922 Crowell 294-64 X 2,803,559 8/1957 Rutherfurd et al. 1l8620 X 3,179,535 4/1965 Comtois 117-212. X

FOREIGN PATENTS 136,151 4/ 1961 Russia.

CHARLES A. WILLMUTH, Primary Examiner. PETER FELDMAN, Assistant Examiner. 

1. IN AN APPARATUS FOR TERMINATING FILM RESISTORS WITHOUT DEGRADING THE RESISTIVE FILM, CONVEYANCE MEANS FOR ADVANCING SAID RESISTORS AT A DETERMINED RATE THROUGH A PLURALITY OF WORK STATIONS, SAID CONVEYANCE MEANS COMPRISING A ROTATABLE MAIN WHEEL HAVING A PLURALITY OF SPACED PERIPHERAL SERRATIONS, FEED MEANS FOR INTRODUCING SAID RESISTORS INTO SAID SERRATIONS, MEANS RETAINING SAID RESISTORS IN SAID SERRATIONS, APPLICATOR MEANS FOR APPLYING A CONDUCTIVE LIQUID MEDIUM ONTO THE ENDS OF EACH OF SAID RESISTORS, SAID APPLICATOR MEANS COMPRISING A PLURALITY OF ROTATING WHEELS, MEANS FOR INTRODUCING SAID CONDUCTIVE LIQUID MEDIUM INTO A CIRCUMFERENTIAL GROOVE CARRIED BY EACH OF SAID PLURALITY OF WHEELS, SAID CONDUCTIVE LIQUID MEDIUM RETAINED IN SAID GROOVES BY CAPILLARY ATTRACTION, MEANS DISPOSED ADJACENT THE BASE OF EACH OF SAID GROOVES AND ADAPTED TO PLACE SAID CONDUCTIVE LIQUID MEDIUM OVER SAID RESISTOR ENDS AS SAID PLURALITY OF WHEELS ROTATE THEREOVER, A HEATING ELEMENT ADJACENT SAID MAIN WHEEL ADAPTED TO DRY SAID CONDUCTIVE MEDIUM ON THE ENDS OF SAID RESISTORS, AND INDUCTION HEATING COIL MEANS FIRING SAID CONDUCTIVE MEDIUM TO FORM A SOLDERABLE TERMINATION ON EACH END OF SAID RESISTOR WITHOUT DEGRADING THE RESISTIVE FILM OF SAID RESISTORS, AND TRIPPING MEANS ATTACHED TO REMOVE SAID RESISTORS HAVING SOLDERABLE END TERMINATIONS FROM SAID MAIN WHEEL PRIOR TO REACHING SAID FEED MEANS. 